A pneumatic, or air-filled, tire is made of an airtight inner core filled with pressurized air or nitrogen. A tread, usually reinforced with steel belting or other materials, covers this inner core and provides the contact area with the traction surface. The pressure of the air inside the tire is greater than atmospheric air pressure, so that the tire remains inflated even with the weight of a machine resting on it. The air pressure within tires provides a cushioning effect and resistance, sometimes called “air springs”, to radial, lateral, and torsion forces that try to deform the tire as the tire hits bumps and holes. A puncture of a pneumatic tire could result in loss of machine traction, control, and stability.
Pneumatic tires also undergo variances in air pressure and tire performance. The pressure inside the tires maintains the radial and lateral stiffness and effective spring rate of the tires. Lower tire pressure (lower spring rate) can create improved traction and increased comfort since the tires “flatten” slightly and increase the contact with the traction surface. A lower spring rate, however, can also reduce machine stability, reduce handling capability and increase rolling resistance due to added radial and lateral deflections. Higher tire pressures (higher spring rates) can reduce rolling resistance, but traction may be reduced creating a potential loss of control.
Many machine users do not set and maintain their tire pressure properly. This may result in improper machine orientation, and spatial attitude, thereby creating situations which could result in loss of control or stability.
Pneumatic tires are also susceptible to changes in temperature, which can change the tire's internal pressure and spring rate. Over-inflation may increase the potential for a tire or wheel rim rupture. In addition, pneumatic tires are inherently plagued with variations in loaded rolling radii, and this condition is typically amplified with increased tire pressures. This variation in rolling radii creates uneven instantaneous heights (single wheel/tire) and uneven side-to-side heights (multiple wheel/tires) leading to reduced implement performance. For example, uneven side-to-side heights in a riding mower may result in uneven cuts due to an out of level cutting deck as well as operator discomfort due to vibration and bounce.